1. Field of the Invention
The invention relates to a procedure and system for detecting when a person falls. It will be especially useful in medical institutions taking care of elderly people.
2. Discussion of the Background
There already exists a wide range of systems and procedures that monitor a person's activity and even detect a critical state requiring intervention. In general, one or more sensors are placed on the person and these continually transmit signals about his/her physical activity. Such signals typically take measurements of acceleration in one or more directions: hence a fall appears as a sharp change, generally involving a series of oscillations of short duration in at least one of the acceleration signals. An example of this is patent U.S. Pat. No.-B2-6,703,939.
One pitfall frequently encountered with systems of this kind is that it is difficult to determine what kinds of things have happened to the person wearing the sensor from the signals that it transmits. If a fall is characterized by an acceleration in the vertical direction, then actions involving bending or sitting give a similar response. When lying down the wearer naturally reproduces a movement that resembles a fall. Certain criteria distinguishing between an accidental fall and normal activities have been identified, but they are inadequate. Hence improvements are eagerly awaited by specialists. The invention represents such an improvement. In the procedure detecting a fall, measurement of the acceleration signal is supplemented by measuring signals of a different kind, whose combination gives a more reliable indication of the fall.